text: The thermodynamics of the host and guest interaction can be assessed by NMR spectroscopy, UV/visible spectroscopy, and isothermal titration calorimetry. Quantitative analysis of binding constant values provides useful thermodynamic information.
  An association constant,  can be defined by the expression
  where {HG} is the thermodynamic activity of the complex at equilibrium. {H} represents the activity of the host and {G} the activity of the guest. The quantities ,  and  are the corresponding concentrations and  is a quotient of activity coefficients.
  In practice the equilibrium constant is usually defined in terms of concentrations. 
  When this definition is used, it is implied that the quotient of activity coefficients has a numerical value of one. It then appears that the equilibrium constant,  has the dimension 1/concentration, but that cannot be true since the standard Gibbs free energy change,  is proportional to the logarithm of K.
  This apparent paradox is resolved when the dimension of  is defined to be the reciprocal of the dimension of the quotient of concentrations. The implication is that  is regarded as having a constant value under all relevant experimental conditions. Nevertheless it is common practice to attach a dimension, such as millimole per litre or micromole per litre, to a value of K that has been determined experimentally.
  A Large  value indicates that host and guest molecules interact strongly to form the host–guest complex.